1. Field of the Invention
The present invention generally relates to a metal/ceramic bonding article having a ceramic substrate and a metal member bonded to the ceramic substrate, and a method for producing the same. More specifically, the invention relates to a metal/ceramic bonding article wherein a metal member of a copper alloy serving as a resistive element is bonded to a ceramic substrate and which is used for an electronic member for resistance, such as a shunt resistive element, and a method for producing the same.
2. Description of the Prior Art
In conventional electronic members for resistance, such as shunt resistive elements, an alloy plate, such as a manganin alloy plate, which serves as a sheet resistor precisely worked by a press working or the like, is bonded to a ceramic substrate, such as an alumina substrate, by the brazing and soldering using a brazing filler metal, such as a silver solder, which contains an active metal (see, e.g., Japanese Patent Laid-Open No. 11-97203).
On the other hand, as methods for bonding a metal plate directly to a ceramic substrate without the need of any intermediate materials, such as brazing filler metals, there are a so-called eutectic bonding method for heating a metal plate and a ceramic substrate at a temperature between their eutectic point and the melting point of the metal in an atmosphere of an inert gas to produce an eutectic melt between the metal plate and the ceramic substrate to bond the metal plate directly to the ceramic substrate (see, e.g., Japanese Patent Laid-Open No. 52-37914), and a so-called molten metal bonding method for causing a molten metal to contact a ceramic substrate to bond a metal plate directly to the ceramic substrate (see, e.g., Japanese Patent Laid-Open No. 7-193358).
However, in the brazing and soldering which uses a brazing filler metal containing an active metal, it is required to use a noble metal, such as silver, as the active metal, so that there is a problem in that production costs are increased. In addition, there are some cases where the brazing and soldering are not preferably used for preparing electronic members for resistors, since resistance varies due to the alloying of the alloy metal with the brazing filler metal. Moreover, if an alloy plate of a copper-nickel alloy, a copper-nickel-manganese alloy or the like is bonded to a ceramic substrate by a brazing filler metal, there are some cases where reliability necessary for electronic members can not be obtained due to hardness (strength) of the brazing filler metal and due to stress produced by a difference in thermal expansion coefficient between the brazing filler metal and the ceramic substrate.
The eutectic bonding method can be only used for bonding a metal plate and a ceramic substrate which produce an eutectic melt, and often utilizes oxygen in a ceramic as a bonding material, so that it is difficult to bond a metal to a non-oxide ceramic.
The molten metal bonding method is designed to cause a molten metal to contact a ceramic substrate to bond a metal plate directly to the ceramic substrate, so that there are some cases where it is difficult to produce an electronic material having a fine shape, such as a resistor.